Improve error handling and validation in importantVocab computed property of VocabLessonView

- Added checks to ensure importantVocab is only processed if lesson and grammarExercises are valid.
- Enhanced error handling with try-catch blocks to log issues during vocabulary extraction, improving robustness.
- Updated the condition for rendering the vocabulary list to prevent errors when importantVocab is undefined.

frontend/src/views/social/VocabLessonView.vue

@@ -39,7 +39,7 @@
         </div>
 
         <!-- Wichtige Begriffe aus den Übungen -->
-        <div v-if="importantVocab.length > 0" class="vocab-list">
+        <div v-if="importantVocab && importantVocab.length > 0" class="vocab-list">
           <h4>{{ $t('socialnetwork.vocab.courses.importantVocab') }}</h4>
           <div class="vocab-items">
             <div v-for="(vocab, index) in importantVocab" :key="index" class="vocab-item">
@@ -196,11 +196,15 @@ export default {
     },
     importantVocab() {
       // Extrahiere wichtige Begriffe aus den Übungen
-      if (!this.lesson || !this.lesson.grammarExercises) return [];
+      try {
+        if (!this.lesson || !this.lesson.grammarExercises || !Array.isArray(this.lesson.grammarExercises)) {
+          return [];
+        }
         
         const vocabMap = new Map();
         
         this.lesson.grammarExercises.forEach(exercise => {
+          try {
             // Extrahiere aus questionData
             const qData = this.getQuestionData(exercise);
             const aData = this.getAnswerData(exercise);
@@ -228,9 +232,16 @@ export default {
                 vocabMap.set(correct, { learning: correct, reference: correct });
               }
             }
+          } catch (e) {
+            console.warn('Fehler beim Extrahieren von Vokabeln aus Übung:', e);
+          }
         });
         
         return Array.from(vocabMap.values());
+      } catch (e) {
+        console.error('Fehler in importantVocab computed property:', e);
+        return [];
+      }
     }
   },
   computed: {